November 21, 2011

A team of six scientists from Portugal began their article noting “According to the Intergovernmental Panel on Climate Change, the concentration of carbon dioxide [CO2] in the atmosphere has been increasing since pre-industrial times and is expected to exceed 550 ppm by the middle of the twenty-first century as a direct result of human activities, primarily fossil fuel burning, cement production and modified land-use patterns. More frequent extreme weather is therefore predicted by most models, along with a significant increase of the summer air temperature and water stress, namely for regions with a Mediterranean-type environment. Expected changes in the climate of viticultural regions may alter significantly both the spectrum and the distribution of grape varieties currently used. In particular, shifts in precipitation patterns will affect most European regions, with increased risk of drought and, given this scenario, the consequences would be most dramatic for the Iberian Peninsula”.

We could and have addressed their concerns about climate change many times, but we found ourselves interested in their focus on how elevated CO2 concentrations will impact grapes growing in the Douro Region of Portugal. Moutinho-Pereira et al. state “Red wine produced in Demarcated Douro Region (Oporto wine region) is one of the most important products for the Portuguese economy.”

Given their interest in grapes and elevated CO2, the team grew grapes in open-top chambers for three years (2004, 2005, 2006) with ambient (365 ppm) and elevated (500 ppm) atmospheric CO2 concentrations. Among many other findings, the team found that the elevated CO2 concentration increased net photosynthetic rate, intrinsic water use efficiency and leaf thickness—the grapevines loved the higher levels of CO2! We know what you are thinking – what about the yield? Well, in 2004, the elevated CO2 increased the yield by 50%, in 2005 by 27%, and in 2006 by 50%. Moutinho-Pereira et al. conclude “The yield per vine showed a clear tendency to increase in elevated [CO2] in the 3 growing seasons (P < 0.1) and this increase was mainly due to an increase in the average cluster weight”. We’ll drink to that great news!

But wait – the news is even better than you thought! A team of scientists from Portugal and Germany approached the future of grapes in the Douro Region using an entirely different methodology. Santos et al. begin their article in the International Journal of Biometeorology noting “Globally, Portugal is the 11th highest wine-producing country (approximately 3% of global production in 2006) and 5th in the European Union. Among the Portuguese wine production areas, the Douro Region produces the world famous Port Wine and other remarkably high-quality table wines. Most importantly, Port Wine accounts for more than 60% of the total value of wine exports and roughly 12% of national wine production.” Wine is definitely big business in Portugal, and we are not surprised that the research was funded “by the project Sustentabilidade da Viticultura de Encosta nas Regiões do Douro e do Duero, Programa Operacional de Cooperação Transfronteiriça Espanha-Portugal.”

The Santos et al. team remind us that “Atmospheric factors, such as temperature, precipitation and radiation, strongly control grapevine growth and development, primarily by affecting photosynthetic rate. Photosynthesis is also stimulated by increasing CO2 concentration, which may result in greater accumulation of total biomass and harvestable yield”. These scientists decided to skip over the benefits of elevated CO2 and focus entirely on how future changes in climate might influence the grape yield.

They collected grape yield data from the Demarcated Region of Douro (DRD) over the period 1986 to 2008; they also collected monthly temperature and precipitation data for the area over the same time period. They conducted a variety of statistical tests and found that highly statistically significant correlations exist between the climate variables and the yield data. They used multiple regression to develop their grapevine yield model (GYM) and found more than 50% of the variance in yield could be explained by the temperature and precipitation variables. The plants seemed to do especially well when March was wet, May and June were dry, and when May and June were warmer than normal.

You probably see where this is going? Next, they gathered projections from the Intergovernmental Panel on Climate Change of what is expected in the way of climate change for the DRD over the next 100 years. Run the projections through the GYM, and just like magic, they produced estimates of future grape yields. You guessed it – the models are indeed predicting changes that should benefit the vines.

Santos et al. state “the projected changes in predictors have direct implications for the modeled yield. Reduction in May and June precipitation, stabilization of March precipitation and increases in May and June temperatures jointly imply an increase in projected yield. In fact, combining all changes in the five predictors, GYM-derived yield is expected to undergo a sustained upward trend, which is particularly clear in the second half of the twenty-first century”. The authors conclude “grapevine yield in the DRD is expected to undergo an upward trend until the end of this century, which might be further enhanced by projected upward trends in CO2 concentration.”

Put these two articles together and a very positive picture emerges for the future of grapes in the DVD. To be fair, Santos et al. warn us that changes in the grapevines may alter the quality of wine products in the future. One of the possible outcomes could be “unbalanced wines with little acidity and excessive alcohol, particularly in the eastern and warmer part of the DRD”. We will all have to deal with the excessive alcohol problem when the time comes!

And while we’re not particularly fond of climate models projections, and even less so when they are regionally-downscaled, the point here is that there are plenty of positive outcomes that are being posited from projected climate changes—however, these type of outcomes never seem to make it into the mainstream press.